Re: [PATCH] mm: check the return value of lookup_page_ext for all call sites

Shi, Yang
2016-05-27T20:17:23Z

On 5/27/2016 1:02 PM, Andrew Morton wrote:
> On Thu, 26 May 2016 16:15:28 -0700 "Shi, Yang" <yang.shi@linaro.org> wrote:
>
>>>>
>>>> I hope we consider this direction, too.
>>>
>>> Yang, Could you think about this?
>>
>> Thanks a lot for the suggestion. Sorry for the late reply, I was busy on
>> preparing patches. I do agree this is a direction we should look into,
>> but I haven't got time to think about it deeper. I hope Joonsoo could
>> chime in too since he is the original author for page extension.
>>
>>>
>>> Even, your patch was broken, I think.
>>> It doesn't work with !CONFIG_DEBUG_VM && !CONFIG_PAGE_POISONING because
>>> lookup_page_ext doesn't return NULL in that case.
>>
>> Actually, I think the #ifdef should be removed if lookup_page_ext() is
>> possible to return NULL. It sounds not make sense returning NULL only
>> when DEBUG_VM is enabled. It should return NULL no matter what debug
>> config is selected. If Joonsoo agrees with me I'm going to come up with
>> a patch to fix it.
>>
>
> I've lost the plot here. What is the status of this patch?
>
> Latest version:

Yes, this is the latest version. We are discussing about some future
optimization.

And, Minchan Kim pointed out a possible race condition which exists even
before this patch. I proposed a quick fix, as long as they are happy to
the fix, I will post it to the mailing list.

Thanks,
Yang

>
> From: Yang Shi <yang.shi@linaro.org>
> Subject: mm: check the return value of lookup_page_ext for all call sites
>
> Per the discussion with Joonsoo Kim [1], we need check the return value of
> lookup_page_ext() for all call sites since it might return NULL in some
> cases, although it is unlikely, i.e. memory hotplug.
>
> Tested with ltp with "page_owner=0".
>
> [1] http://lkml.kernel.org/r/20160519002809.GA10245@js1304-P5Q-DELUXE
>
> [akpm@linux-foundation.org: fix build-breaking typos]
> [arnd@arndb.de: fix build problems from lookup_page_ext]
> Link: http://lkml.kernel.org/r/6285269.2CksypHdYp@wuerfel
> [akpm@linux-foundation.org: coding-style fixes]
> Link: http://lkml.kernel.org/r/1464023768-31025-1-git-send-email-yang.shi@linaro.org
> Signed-off-by: Yang Shi <yang.shi@linaro.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> include/linux/page_idle.h | 43 ++++++++++++++++++++++++++++++------
> mm/page_alloc.c | 6 +++++
> mm/page_owner.c | 26 +++++++++++++++++++++
> mm/page_poison.c | 8 +++++-
> mm/vmstat.c | 2 +
> 5 files changed, 77 insertions(+), 8 deletions(-)
>
> diff -puN include/linux/page_idle.h~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites include/linux/page_idle.h
> --- a/include/linux/page_idle.h~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
> +++ a/include/linux/page_idle.h
> @@ -46,33 +46,62 @@ extern struct page_ext_operations page_i
>
> static inline bool page_is_young(struct page *page)
> {
> - return test_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return false;
> +
> + return test_bit(PAGE_EXT_YOUNG, &page_ext->flags);
> }
>
> static inline void set_page_young(struct page *page)
> {
> - set_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return;
> +
> + set_bit(PAGE_EXT_YOUNG, &page_ext->flags);
> }
>
> static inline bool test_and_clear_page_young(struct page *page)
> {
> - return test_and_clear_bit(PAGE_EXT_YOUNG,
> - &lookup_page_ext(page)->flags);
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return false;
> +
> + return test_and_clear_bit(PAGE_EXT_YOUNG, &page_ext->flags);
> }
>
> static inline bool page_is_idle(struct page *page)
> {
> - return test_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return false;
> +
> + return test_bit(PAGE_EXT_IDLE, &page_ext->flags);
> }
>
> static inline void set_page_idle(struct page *page)
> {
> - set_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return;
> +
> + set_bit(PAGE_EXT_IDLE, &page_ext->flags);
> }
>
> static inline void clear_page_idle(struct page *page)
> {
> - clear_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return;
> +
> + clear_bit(PAGE_EXT_IDLE, &page_ext->flags);
> }
> #endif /* CONFIG_64BIT */
>
> diff -puN mm/page_alloc.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_alloc.c
> --- a/mm/page_alloc.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
> +++ a/mm/page_alloc.c
> @@ -656,6 +656,9 @@ static inline void set_page_guard(struct
> return;
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + return;
> +
> __set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
>
> INIT_LIST_HEAD(&page->lru);
> @@ -673,6 +676,9 @@ static inline void clear_page_guard(stru
> return;
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + return;
> +
> __clear_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
>
> set_page_private(page, 0);
> diff -puN mm/page_owner.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_owner.c
> --- a/mm/page_owner.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
> +++ a/mm/page_owner.c
> @@ -55,6 +55,8 @@ void __reset_page_owner(struct page *pag
>
> for (i = 0; i < (1 << order); i++) {
> page_ext = lookup_page_ext(page + i);
> + if (unlikely(!page_ext))
> + continue;
> __clear_bit(PAGE_EXT_OWNER, &page_ext->flags);
> }
> }
> @@ -62,6 +64,7 @@ void __reset_page_owner(struct page *pag
> void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
> {
> struct page_ext *page_ext = lookup_page_ext(page);
> +
> struct stack_trace trace = {
> .nr_entries = 0,
> .max_entries = ARRAY_SIZE(page_ext->trace_entries),
> @@ -69,6 +72,9 @@ void __set_page_owner(struct page *page,
> .skip = 3,
> };
>
> + if (unlikely(!page_ext))
> + return;
> +
> save_stack_trace(&trace);
>
> page_ext->order = order;
> @@ -82,6 +88,8 @@ void __set_page_owner(struct page *page,
> void __set_page_owner_migrate_reason(struct page *page, int reason)
> {
> struct page_ext *page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + return;
>
> page_ext->last_migrate_reason = reason;
> }
> @@ -89,6 +97,12 @@ void __set_page_owner_migrate_reason(str
> gfp_t __get_page_owner_gfp(struct page *page)
> {
> struct page_ext *page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + /*
> + * The caller just returns 0 if no valid gfp
> + * So return 0 here too.
> + */
> + return 0;
>
> return page_ext->gfp_mask;
> }
> @@ -99,6 +113,9 @@ void __copy_page_owner(struct page *oldp
> struct page_ext *new_ext = lookup_page_ext(newpage);
> int i;
>
> + if (unlikely(!old_ext || !new_ext))
> + return;
> +
> new_ext->order = old_ext->order;
> new_ext->gfp_mask = old_ext->gfp_mask;
> new_ext->nr_entries = old_ext->nr_entries;
> @@ -193,6 +210,11 @@ void __dump_page_owner(struct page *page
> gfp_t gfp_mask = page_ext->gfp_mask;
> int mt = gfpflags_to_migratetype(gfp_mask);
>
> + if (unlikely(!page_ext)) {
> + pr_alert("There is not page extension available.\n");
> + return;
> + }
> +
> if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
> pr_alert("page_owner info is not active (free page?)\n");
> return;
> @@ -251,6 +273,8 @@ read_page_owner(struct file *file, char
> }
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + continue;
>
> /*
> * Some pages could be missed by concurrent allocation or free,
> @@ -317,6 +341,8 @@ static void init_pages_in_zone(pg_data_t
> continue;
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + continue;
>
> /* Maybe overraping zone */
> if (test_bit(PAGE_EXT_OWNER, &page_ext->flags))
> diff -puN mm/page_poison.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_poison.c
> --- a/mm/page_poison.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
> +++ a/mm/page_poison.c
> @@ -54,6 +54,9 @@ static inline void set_page_poison(struc
> struct page_ext *page_ext;
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + return;
> +
> __set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> }
>
> @@ -62,6 +65,9 @@ static inline void clear_page_poison(str
> struct page_ext *page_ext;
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + return;
> +
> __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> }
>
> @@ -70,7 +76,7 @@ bool page_is_poisoned(struct page *page)
> struct page_ext *page_ext;
>
> page_ext = lookup_page_ext(page);
> - if (!page_ext)
> + if (unlikely(!page_ext))
> return false;
>
> return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> diff -puN mm/vmstat.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/vmstat.c
> --- a/mm/vmstat.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
> +++ a/mm/vmstat.c
> @@ -1061,6 +1061,8 @@ static void pagetypeinfo_showmixedcount_
> continue;
>
> page_ext = lookup_page_ext(page);
> + if (unlikely(!page_ext))
> + continue;
>
> if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
> continue;
> _
>